In more than 40 episodes spanning 75 years, equity and bond fund investors have defied predictions that they would panic and spark crises. Yet banking regulators won’t let go of their “run” scenario. Why?

LONDON — Theresa May said she has secured an "improved Brexit deal" that "deserves the support of every" MP, even as it became clear that key groups in the House of Commons had abandoned her.

Opening a debate that will end this evening with a second vote on her Brexit deal, May said she has secured "legally binding changes" to the Northern Ireland backstop since MPs rejected her deal by 230 votes at the first time of asking in January.

But the chances of the deal passing Tuesday evening's vote in the House of Commons have already plummeted after Brexiteer MPs and the Democratic Unionist Party both said they would not back it.

A panel of Brexiteer lawyers, whose advice was seen as crucial to bringing the European Research Group of Conservative backbenchers onboard, recommended MPs not support the deal. Shortly after, a DUP spokesman confirmed the party would also refuse to back it.

The DUP spokesman said it is "clear that the risks remain that the U.K. would be unable to lawfully exit the backstop were it to be activated."

"The European Union has been intransigent. It is possible to reach a sensible deal which works for the United Kingdom and the European Union but it will require all sides to be reasonable and in dealmaking mode," the spokesman added.

Veteran Brexiteer Bill Cash, a member of the panel of Brexiteer lawyers, said: "In the light of our own legal analysis and others we do not recommend accepting the government's motion today."

Their analysis rejected the deal, saying it delivers no changes to the Withdrawal Agreement or Political Declaration, nor a unilateral mechanism by which the U.K. could leave the backstop.

The twin verdicts, which will almost certainly prove fatal for May's deal, came after Attorney General Geoffrey Cox said that despite new assurances secured in last-minute talks in Strasbourg Monday night, "the legal risk remains unchanged" that the U.K. would be unable to leave the backstop unless it could prove the EU had acted in bad faith in its future negotiations.

If the deal is defeated, MPs will vote Wednesday on whether they are prepared to leave the EU with no deal on the current legal date, March 29. If that proposition is rejected, MPs will vote, most likely Thursday, on whether they want to extend the Article 50 negotiating period, delaying Brexit.

European Commission President Jean-Claude Juncker said Monday that any extension could not go beyond May 23, unless the U.K. is prepared to take part in the European election.